I just did this swap.. you are going to need a new motor mount on the passenger side.. as well as use the other DA motor mounts on the 98 engine
Take off the intake manifold, and distributor from the DA.. and connect them to the 98LS.. they line up perfectly.
You are going to have to swap alternators, because the plugs are not the same
there are 3 plugs in the back of the block.. two for sensing oil and coolant temperatures for turning on the fans.. and the other is the oil sending plug.. the oil sending plug , plugs right in.. the oil temperature sensor you do not use.. and the coolant sensor you have to switch pig tails because the 98LS fan temperature sensor is located on the thermostat housing..
basically you are just trading blocks.. if you are using the 98LS transmission you are going to need a clutch cable/ to hydro kit which innovative sells..
There is an extra coolant hose on the 91 da intake manifold and themrostat housing... it connects to this stupid useless valve that lets air in when detecting normal opperating temperatures.. The 94+ LS intake manifolds do not use this.. You can swap thermostat housings.. or do what i did and just block the extra coolant hoses with a screw/ or round object and clamp
any more questions let me know my AIM is beretta2211